Mass spectrometry (MS) has become an important method in analytical chemistry due to its high molecular specificity in combination with very wide applicability, speed, sensitivity and quantitative capability. The development of electrospray ionization has meant that virtually any type of molecule can be ionized and analyzed by MS. However, there are limitations to mass spectrometry. For example, mass spectrometers have typically been large bench-top instruments, found only in laboratories, incapable of use for point-of-care needs. That limitation has led to the development of much smaller (miniature) mass spectrometers that can be operated outside the laboratory (Badman et al., J. Mass Spectrom., 35 (2000) 659-671).
Another limitation of mass spectrometry is that the sampling and ionization sequence most used in MS experiments is too slow. To address that limitation, MS analysis without any sample preparation was developed (ambient MS or more often ambient ionization) (Cooks et al., Science, 311 (2006) 1566-1570). Ambient ionization has proven durable with many variations being introduced and some being commercialized over the past decade (Harris et al., Analytical Chemistry, 83, 4508-4538 (2011); and Ambient Ionization Mass Spectrometry, Marek Domin & Robert Cody (Eds.) Royal Society of Chemistry, Cambridge, UK, 2015). The two concepts of miniature mass spectrometers and ambient ionization are closely linked in that in situ (on site, point-of-care) mass spectrometry requires both a small instrument and a simplified sampling/ionization routine (Cooks et al., Faraday Disc., 2011, 149 (1), 247-267).
Even with the advent of miniature mass spectrometers and ambient ionization techniques, there are still limitations to mass spectrometry that need to be addressed. Mainly, the most important step in mass spectrometry, mass analysis, cannot be performed at atmospheric pressure. All previous approaches to mass-to-charge (m/z) measurements on ionized atoms, molecules or molecular clusters have been based on operations in vacuum. A general solution to the problem of molecular ion ambient mass analysis is lacking.